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Hydrogen boilers or air source heat pumps?



A consumer guide to the future of heating

For UK households, the next 5-30 years will be a transition to one of a mix of possible heat sources including ‘green gas’ boilers (biomethane/hydrogen) and air source heat pumps. If you are buying a brand new home in the next 1-5 years, it is likely to have an air source heat pump already fitted.

What does this mean for the 22.5 million households on mains gas boilers? We explain these new technologies, when they are suitable, running costs and what it means for you, in our ultimate guide to the future of domestic heating.

What is driving the future of heating? Our net zero 2050 target.

The UK Government has set into law an ambitious target to reduce all greenhouse gases to zero by 2050. The recent refusal of Heathrow’s third runway proves they are serious.

Greenhouses gases from UK homes account for 20% of all emissions, so this is an important area for improvement. Work is already proposed to improve insulation measures in new build homes under the Government’s Future Homes Standard.

This year's Budget announcement also included proposals to replace natural gas with low carbon sources, including hydrogen boilers and air source heat pumps. Finding low carbon heat sources will be crucial to decarbonising the existing housing stock.

Hydrogen Boilers V Air Source Heat Pumps

The domestic heating industry is already gearing up for the changes with two clear ‘camps’ – those that manufacture and fit gas boilers and those that manufacturer and fit air source heat pumps. We have reviewed the viability of both technologies and the implications for UK households.

Team Hydrogen

Existing gas boiler manufacturers are developing ‘hydrogen ready’ boilers; although they are still being tested. If successful and viable, a 100% hydrogen network could prove to be a mass solution for existing homes, which has clear benefits for everyone.

We have considered the overall impact of the changes on households, industry and energy supply infrastructure.

Consumer disruption score - low

Consumer impact could be very low. Consumers will not experience a great deal of disruption to supplies or how they receive heating. Hydrogen boilers will work in much the same way as gas boilers and look much the same. As such they are about as close to a direct replacement as possible.

There will be a process of conversion and for the householder this will take the form of changing parts on an existing boiler to changing the boiler. The aim is to produce hydrogen ready boilers soon to aid the change over as the new network is rolled out.

At ground level, every property will require an initial survey to check the adequacy of existing pipework. Whilst hydrogen is still a gas, it is more prone to leaking and potentially more explosive. The speed of its roll out will also depend on the speed with which engineers can be trained.

Fuel costs impact score – unknown, but likely rising from current low levels

Whilst 20% hydrogen can be mixed into our existing gas supplies and run on existing boilers, it will require some infrastructure changes and an additional process to create the hydrogen. Overall the price for fossil fuels is likely to rise to level the playfield for decarbonised electricity.

For a full hydrogen network, all supplies will need to be upgraded at a significant cost to the national finances. Full prices will undoubtedly rise to recoup this investment.

Industry impact score - low/medium

The existing gas industry is well placed to adapt to hydrogen. By producing the same sort of boiler product, boiler manufacturers ensure their long term survival without any real significant changes to their manufacturing processes.

Existing Gas Safe registered engineers will do a ‘bolt-on’ qualification as part of their Gas Safe registration but not have to change technologies.

However it is not as simple as swapping one fuel out for another to solve endemic problems across the sector. The industry cannot treat hydrogen as a quick fix to the failings of the last 15 years. Condensing gas boilers rarely run at their A-rated efficiencies due to poor practices across the industry. This must be addressed as a priority before we swap one fuel out for another.

National cost - high

The main barriers to hydrogen is the cost of a brand new national network to replace the existing gas pipe supply network. This will come at some cost, financially and environmentally. It will also require hydrogen production on a huge scale. The ‘carbon neutrality’ of hydrogen depends on how it is generated and also requires carbon capture and storage to achieve its renewable status.

Team Air Source

Air source heat pumps on the other hand are an established and proven technology. They run on electricity and for every unit of electricity they use they generate 2-4 units of energy ‘free’ from the air.

As electricity increasingly comes from green sources (wind farms and biomass fuelled power stations) so they are considered an excellent solution to decarbonising our homes.

It is worth pointing out that one barrier that does not exist is the assertion that heat pumps are unsuitable for older properties. The Carbon Trust state that the average UK home needs just 6kW of heat on a very cold day. Heat pump outputs range between 3kW and 16kW so can comfortably heat most UK homes.

Consumer disruption score – low/medium

The impact on consumers is disruptive if the installation of a low temperature heat pump will require changing all our radiators for much larger units. However the levels of disruption for all households by way of increased insulation measures is unavoidable, so that a heat pump installation is simply par for the course.

If insulation is a success then we may not have to change our existing radiators, however the internal equipment is bigger than the compact combi boilers we have all got so used to and we may have to give up our airing cupboard to a cylinder once again.

At present the cost of a heat pump without any significant government subsidy is 3 – 6 times that of a gas boiler. Currently households can claim back £5,000 via the Green Homes Grant and claim the balance of the Renewable Heat Incentive over a 7 year period. This does a great job of reducing the cost to something close to that of a new gas boiler.

Fuel costs impact score – unknown but likely rising from current low levels

At present, electricity costs 12.5p per kW hour compared with gas at around 3.5p per kW hour. However the running costs can be in line with gas boilers because of the proportion of free energy they generate (providing they are set up correctly).

To encourage more people onto greener fuels, the 2020 Budget states that the cost of fuel will reflect its level of carbon emissions, which will see electricity prices falling and fossil fuel prices rising.

Industry impact score - high

There are simply not enough trained heating engineers or air conditioning engineers to fit heat pumps at the scale needed. The roll out of heat pumps relies on us up-skilling 100,000 or so domestic gas and oil engineers to fit them and that is a huge undertaking made worse by the existing skills gap for condensing gas boilers.

The core problem here is that 99% of installers are not trained in heating system design and this knowledge is vital to setting up heat pumps to run that their label efficiencies or close to. 99% of gas installer already get condensing gas boilers wrong because they were not up-skilled in condensing, low temperature heating.

Gas boilers still work so no-one is any the wiser, however heat pumps have a much smaller margin for error and will get very expensive to run very fast if we are as casual with their installation as we are with gas boilers.

The industry must take engineer skill serious if we are achieve actual efficiencies that get us to net zero, not the on-paper efficiencies of the last 15 years that fall way short.

National cost - high

The technology is not without its barriers however. Whilst they could run off the existing electricity grid, they existing grid would need significantly ‘beefing-up’ in order to run 22.5 million new heat pumps.

Short term changes

In the short term it looks feasible that 20% of a hydrogen can be injected into exist supplies and most modern boilers will cope (tests are ongoing), but this would only reduce our greenhouse gases by 6-10%.

Heat pumps seem to be just a little further progressed in terms of rolling out in large numbers, so we must start up-skilling installers now and to a level that guarantees label efficiencies, not just meeting installation targets.

Where the government plans fall down is addressing the inefficiency of existing heating systems. Condensing boilers became mandatory in 2005, but 15 years later very few operate at the efficiencies on the label (90% or more). Average efficiencies according to The Energy Saving Trust are more like 80%.

EPC reports still encourage householders to upgrade to a condensing boilers from a non-condensing boilers to improve the energy banding of their homes. As late non-condensing models were around 78% efficient so the improvement is likely to be negligible.

There are many reasons behind our failure to make condensing boilers condense (which is when they operate at their most efficient), but certainly boiler oversizing, incompatible smart controls that are not ‘smart’ and weak legislation are all in the mix. What is clear is that putting this right is not only an easy win, it’s a cheap win. We are campaigning for these changes and have set out our recommendations in our Close The Gap Campaign.


Jo Alsop

Heating Hero

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